This invention relates generally to systems for controlling the emissions of pollutants from wood burning stoves. More particularly, this invention relates generally to systems for oxidizing combustibles in the exhaust gases generated by the primary combustion of a wood burning stove.
Environmental and regulatory concerns have resulted in increasing regulation and stricter requirements as to the acceptable level and quality of exhaust emissions which may be generated by wood burning stoves. The Federal Environmental Protection Agency has mandated that wood burning stoves manufactured after July 1, 1988 comply with strict emission standards. Most conventional wood burning stoves do not meet the emission regulations of the Environmental Protection Agency. A number of systems have been advanced for reducing the pollutants of the exhaust gases produced by the primary wood burning combustion. Some systems have involved catalytic converters or combustors for facilitating the secondary combustion of exhaust pollutants. A number of conventional systems which are effective in reducing pollutants are not effective under all conditions such as when the ash pan is opened and an "under fire" condition is produced in the firebox.
Van Dewoestine U.S. Pat. No. 4,373,452 discloses a wood burning stove which employs a catalytic burner converter for oxidizing various uncombusted matter in the exhaust produced by the primary combustion. In one embodiment, the catalytic burner is located in the flue immediately adjacent the combustion chamber of the stove. The catalytic converter may also be situated in the combustion chamber. The catalytic converter is a cellular ceramic honeycomb structure with a plurality of mutually parallel cells extending through the converter. The catalytic converter may have a variety of forms such as a ceramic monolith having an alumina washcoat and coated with a precious metal catalyst such as palladium, platinum or alloys of the materials. A means for providing secondary air in the vicinity of the catalytic converter is also provided to enhance the operation of the catalytic converter.
Catalytic combustors of the type having a ceramic honeycomb substrate and precious metal catalyst coatings have been employed in connection with wood burning stoves for a number of years for facilitating the combustion of products in the exhaust from the primary combustion. The application of catalytic combustors in wood burning technology has engendered a number of problems. For example, non-uniform catalyst temperatures tend to cause cracking of the combustor substrates. The conventional vertical cell orientation for the normal exhaust flow path results in conventional catalyst combustors being vulnerable to premature failure due to the ceramic chips falling out of the combustors. Bulky metal housings also result in the heat up time of the catalytic combustors being relatively slow. The effectiveness of catalytic combustors can also be easily compromised under various conditions.